ANewApproachtoMetalatedImidoand AmidoTellurophosphoranes** Glen G. Briand, Tristram Chivers,* and Masood Parvez Monoanionic ligands of the type [R 2 P(E)NP(E)R 2 ]  1 have been investigated extensively as ligands for both main group elements [1] and transition metals. [2] This widespread interest stems from their potential uses as lanthanide shift reagents, [2] industrial catalysts, [3] luminescent materials, [4] or in metal extraction processes. [5] Recently we [6] and Stahl et al. [7] reported the first ambidentate dianionic ligands [RN(E)P(m- NR) 2 P(E)NR] 2 2, which adopt a variety of bonding modes, that is N,E, N,N’, or E,E’, with metal centers. Despite this intense activity, the tellurium analogues of 1 and 2 are unknown. Anionic tellurophosphinic amides of the type [tBu 2 P(Te)NR]  (R ¼ iPr, Cy) can be prepared by lithiation of [tBu 2 P(Te)NHR] with LinBu, and chelate com- plexes of this anion with Group 12 metals have been inves- tigated as single-source precursors of binary metal tellurides. [8] Although ditellurides of the type [R(Te)P(m-NtBu) 2 P(Te)R] (R ¼ Me, tBu) have been reported, [9] our attempts to oxidize tBuN(H)P(m-NtBu) 2 PN(H)tBu with an excess of elemental tellurium in boiling toluene produced only the monotelluride [tBuNH(Te)P(m-NtBu) 2 PN(H)tBu] in about 5% yield. [10] Endeavors to generate (TePPh 2 ) 2 NH in a similar manner have also been unsuccessful. Consequently, we adopted a different approach to the synthesis of the anionic ligands 1 (E ¼ Te) and 2 (E ¼ Te), which involves metalation of the neutral imido or amido precursor prior to the reaction with tellurium. [11] Herein, we report the synthesis and X-ray structures of [{[Na(tmeda)][(TePPh 2 ) 2 N]} 2 ](3) and [Li(tme- da)] 2 [Te(NtBu)P(m-NtBu) 2 P(NtBu)Te] (4), (tmeda ¼ tetra- methylethylenediamine), which contain the first examples of 1 (E ¼ Te) and 2 (E ¼ Te), respectively. The reaction of Na[Ph 2 PNPPh 2 ] with tellurium powder in hot toluene in the presence of TMEDA produced 3 as moisture-sensitive, yellow crystals in 33% yield. The molec- ular structure of 3 (Figure 1) was determined by X-ray diffraction [12] on crystals obtained from hexane. The ditellur- oimidodiphosphinate ligand 1 (R ¼ Ph, E ¼ Te) is Te,Te’ chelated to sodium and forms a centrosymmetric dimer through Na Te interactions. This is the first example of Te,Te’ chelation to an alkali metal. The coordination sphere of the Na þ ions is completed by one N,N’ chelating tmeda ligand. A similar structure has been reported for the sodium salt of a monothioimidodiphosphinate [{Na(thf) 2 [(OPPh 2 )(SPPh 2 )- N]} 2 ]. [13] The central Na 2 Te 2 ring in 3 is almost square-planar (bond angles at Na1 and Te1 are 87.51(5) and 92.49(5)8, respectively) with Na Te distances of 3.143(2) and 3.181(2) ä, which are close to the value of 3.16 ä predicted from the ionic radii [14] and much shorter than the weak Na Te interactions (3.494(3) ä) in the tellurolate [Na(tme- da) 2 ][Te(2,4,6-Me 3 C 6 H 2 )]. [15] The P Te bond lengths of 2.383(1) and 2.403(1) ä are only slightly longer than the values of about 2.37 ä determined for tBu 3 P ¼ Te [16] and amino-substituted tellurophosphoranes. [9c,17] The shorter P  ZUSCHRIFTEN 3618 ¹ 2002 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim 0044-8249/02/11418-3618 $ 20.00+.50/0 Angew. Chem. 2002, 114, Nr. 18 [12] The structures of racemic 4, 13, and 14 have been determined by X-ray crystallography. CCDC-184691 (4), CCDC-184693 (13), and CCDC- 184694 (14) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam. ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK; fax: (þ 44)1223-336-033; or deposit@ccdc.cam.ac.uk). [13] For examples of other metal-catalyzed asymmetric reactions that show strong solvent effects on enantioselectivity, see: a) Y. Sato, N. Saito, M. Mori, J. Am. Chem. Soc. 2000, 122, 2371; b) M. Ogasawara, H. Ikeda, T. Nagano, T. Hayashi, J. Am. Chem. Soc. 2001, 123, 2089. [14] CCDC-184692 ((1R,2S)-4) contains the supplementary crystallo- graphic data for this paper. [12] The single crystal used for the structure determination was obtained from an optically active sample of 4 with 82% ee. The small absolute structure parameter of 0.15(12) derived from the structure determination confirms the chirality of the crystal. [15] Following the procedures reported by Dauban and Dodd for preparation of iminoiodane PhI ¼NSO 2 (CH 2 ) 2 SiMe 3 from PhI(OAc) 2 and Me 3 Si(CH 2 ) 2 SO 2 NH 2 (P. Dauban, R.H. Dodd, J. Org. Chem. 1999, 64, 5304). [16] 1 H NMR (CDCl 3 , 400 MHz) of 19 : d ¼ 7.89 (d, J ¼ 7.8 Hz, 2H), 7.54 (t, J ¼ 7.4 Hz, 1H), 7.33 (t, J ¼ 7.7 Hz, 2H), 7.16 (m, 4H), 5.19 (m, 1H), 3.06 (m, 4 H). The rather high instability of 19 renders it difficult to characterize this compound fully. [17] The lower ee value in the catalytic reaction than in the reaction between 2 and 19 may arise from a lower loading of 2 in the former case. We once observed that reducing the loading of 2 from 10 to 2 mol % in the amidation of 6 in CH 2 Cl 2 , under otherwise the same conditions, led to a decrease in the ee value of 11 from 46 to 39 %. Notice that some other metal-catalyzed asymmetric reactions also show significant dependence of enantioselectivity on catalyst loading (see for example: H. M. L. Davies, T. Hansen, M. R. Churchill, J. Am. Chem. Soc. 2000, 122, 3063). [*] Prof. T. Chivers, Dr. G. G. Briand, Dr. M. Parvez Department of Chemistry University of Calgary Calgary, AB T2N 1N4 (Canada) Fax: (þ 1)403-289-9488 E-mail: chivers@ucalgary.ca [**] The authors gratefully acknowledge financial support from the Natural Sciences and Engineering Research Council (Canada).